Terminal CO Ligands Research Articles

Revisiting the Synthesis and Elucidating the Structure of Potassium Cyclopentadienyldicarbonylruthenate, K[CpRu(CO)2

Known procedures for the synthesis of K[CpRu(CO)2] (KRp) via reductive cleavage of the ruthenium dimer Rp2 were found to be inconsistent and have thus been revisited, and a revised protocol using K[HB(sec-Bu)3] (K-Selectride) as the reducing agent is now reported that gives yellow KRp in crystalline form in around 40% yield. The structure of KRp·THF has been determined by X-ray diffraction, representing the first crystallographic characterization of an Rp– salt. Inevitably the reductive cleavage of Rp2 also gives a poorly soluble black solid as an additional product, which has now been analyzed by a variety of methods, including 13C MAS NMR spectroscopy using 13CO-labeled material. The black solid has been identified as a polymeric Cp/Ru/CO compound with both bridging and terminal CO ligands in a 3:1 ratio. The present report may stimulate the use of the [CpRu(CO)2]− (Rp–) anion, which has been barely exploited as yet in comparison to its popular congener [CpFe(CO)2]− (Fp–).

Formation of a Hexacarbonyl Diiron Complex Having a Naphthalene-1,8-bis(phenylphosphido) Bridge and the Electrochemical Behavior of Its Derivatives

The P–P bond of the cis-1 ligand in (μ-cis-1)[Fe(CO)4]2 (cis-1 = naphthalene-1,8-diphenyldiphosphine) was cleaved by the two iron centers after CO dissociation from the iron centers, although the P–P bond of cis-1 was stereochemically stabilized with a robust naphthalene group, unlike the usual diphosphines, which lack such support. The resulting (μ-nabip)[Fe(CO)3]2 (3; nabip = naphthalene-1,8-bis(phenylphosphido)) had the diiron core linked by the bisphosphido bridge. Since the trans isomer (μ-trans-1)[Fe(CO)4]2 was stable under ambient conditions, the cis disposition of the two Fe(CO)4 fragments was responsible for the cleavage of the P–P bond. The one or two terminal CO ligands of 3 can be replaced by MeCN and a range of phosphine ligands: i.e., PMe3, PPh3, cis-1, and trans-1. Interestingly, it was found that the diphosphine cis-1 could coordinate the iron center in an unusual κ2 fashion to form a three-membered ring, which was confirmed by NMR spectra as well as X-ray analysis. These diiron complexes ...

2,2′‐Bipyridine and 1,10‐Phenanthroline as Coligands or Structure‐Directing Agents in Uranyl–Organic Assemblies with Polycarboxylic Acids

AbstractSeven uranyl complexes with polycarboxylic acids were synthesized under hydrothermal conditions in the presence of 2,2′‐bipyridine (bipy) or 1,10‐phenanthroline (phen), and their crystal structures were determined. The bipy and phen molecules are uncoordinated in the two oxalate complexes [Hbipy]2[(UO2)2(C2O4)(OH)3]2·bipy (1) and [Hphen]2[(UO2)2(C2O4)3] (2), which provide two new two‐dimensional architectures in the uranyl oxalate family. The first uranyl complexes with citraconic acid (H2citcn) could also be obtained in these conditions: [UO2(citcn)(bipy)] (3) and [UO2(citcn)(phen)] (4) are isomorphous one‐dimensional, ribbonlike polymers in which bipy and phen are terminal coligands. The complex formed with the trans,trans,trans isomer of 1,2,3,4‐cyclobutanetetracarboxylic acid (H4cbtc), [Hbipy][UO2(Hcbtc)]·1.5H2O (5), displays a two‐dimensional arrangement. One of the carboxylic groups retains its proton and is uncoordinated, in contrast to the bonding scheme in the previously reported framework with the same ligand. Bipy is a coligand in the complex with citric acid (H4cit), [(UO2)2(cit)(bipy)]·0.5H2O (6), which contains both the {[UO2(cit)]2}4– dimeric subunits frequently encountered in uranyl citrates and a third uranium centre bound to three carboxylate groups and chelated by bipy. The closely related D‐(–)‐citramalic acid (H3citml) gives the complex [Hphen]2[(UO2)5(citml)4(H2O)]·3H2O (7), a three‐dimensional framework comprising {[UO2(citml)]2}2– dimeric subunits assembled into chains, and other uranium atoms connecting four such chains. Large channels are occupied by columns of Hphen+ counterions held together by π‐stacking interactions. In these complexes, bipy and phen are either present as coligands or as counterions. In the latter case, they act as organic templates that lead to structures different from those previously known with the same carboxylate ligands.

Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(μ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate [Pt3(μ-PBu(t)2)3(CO)2I](+) was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBu(t)2)3I3, the transient 44e(-) species [Pt3(μ-PBu(t)2)3(CO)3](+) is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.

Synthesis and structural characterization of diruthenium cluster containing germylene ligand

Mild thermolysis of arachno-[(Cp*RuCO)2B2H6], 1 in presence of GeCl2·dioxane yielded di-μ-germylene complex [(Cp*Ru)2(μ-GeCl2)2(CO)2], 2 (Cp* = η5-C5Me5). The molecular structure of 2 exhibits a diruthenium unit bridged by a pair of μ-GeCl2 moieties. The Cp* and the terminal CO ligands are oriented in anti fashion with respect to Ru–Ru bond. In addition, the reaction of 2 with arachno-[CpFe(CO)B3H8] (Cp = η5-C5H5) transformed to germenocene, [Cp2Ge:], 3 via an unstable intermediate [CpFe(CO)B2H5GeCl2], I. The 11B NMR spectroscopy was used as a tool to establish a probable reaction pathway for the formation of germenocene 3. Cluster 2 has been characterized by IR and NMR spectroscopy, and the geometric structure was unequivocally established by crystallographic analysis.

Reactivity of Ir(iii) carbonyl complexes with water: alternative by-product formation pathways in catalytic methanol carbonylation

The reactions of water with a number of iridium(III) complexes relevant to the mechanism for catalytic methanol carbonylation are reported. The iridium acetyl, [Ir(CO)2I3(COMe)](-), reacts with water under mild conditions to release CO2 and CH4, rather than the expected acetic acid. Isotopic labeling and kinetic experiments are consistent with a mechanism involving nucleophilic attack by water on a terminal CO ligand of [Ir(CO)2I3(COMe)](-) to give an (undetected) hydroxycarbonyl species. Subsequent decarboxylation and elimination of methane gives [Ir(CO)2I2](-). Similar reactions with water are observed for [Ir(CO)2I3Me](-), [Ir(CO)2(NCMe)I2(COMe)] and [Ir(CO)3I2Me] with the neutral complexes exhibiting markedly higher rates. The results demonstrate that CO2 formation during methanol carbonylation is not restricted to the conventional water gas shift mechanism mediated by [Ir(CO)2I4](-) or [Ir(CO)3I3], but can arise directly from key organo-iridium(III) intermediates in the carbonylation cycle. An alternative pathway for methane formation not involving the intermediacy of H2 is also suggested. A mechanism is proposed for the conversion MeOH + CO → CO2 + CH4, which may account for the similar rates of formation of the two gaseous by-products during iridium-catalysed methanol carbonylation.

Synthesis, characterization, and magnetic studies of a series of metal–mellitate coordination polymers

Benzenehexacarboxylic acid, also known as mellitic acid, reacts readily with cobalt and manganese chlorides to afford a new series of coordination polymers. Three of them are cobalt mellitates (1–3) synthesized at different conditions, i.e. either at room temperature (1) or hydrothermally at 140 (2) and 180 °C (3), the last two in the presence of organic bases. While compound 1 exhibits chains held together by inter-chain hydrogen bonds, compounds 2 and 3 are three-dimensional as could be expected from the synthetic conditions. The latter two structures display complicated connectivity and unusual multi-nodal topologies that have not been observed before. The two manganese compounds contain the nitrogen-based chelating co-ligands 2,2′-bpy or 1,10-phen for 4 and 5, respectively. Due to the pairs of blocked sites by the terminal co-ligands, both structures are low dimensional exhibiting chains in 4 and layers in 5. At the same time, π–π interactions between the co-ligands and multiple inter-chain/layer hydrogen bonds stitch the chains/layers into overall 3D supramolecular frameworks. Magnetic measurements on compounds 2–5 showed that they all exhibit dominant antiferromagnetic coupling. However, the details of the antiferromagnetic behavior are different, and this is consistent with the different structural characteristics.

IR-monitored photolysis of CO-inhibited nitrogenase: a major EPR-silent species with coupled terminal CO ligands.

Fourier transform infrared spectroscopy (FTIR) was used to observe the photolysis and recombination of a new EPR-silent CO-inhibited form of α-H195Q nitrogenase from Azotobacter vinelandii. Photolysis at 4 K reveals a strong negative IR difference band at nu = 1938 cm(-1), along with a weaker negative feature at 1911 cm(-1). These bands and the associated chemical species have both been assigned the label "Hi-3". A positive band at nu = 1921 cm(-1) was assigned to the "Lo-3" photoproduct. By using an isotopic mixture of (12)C (16)O and (13)C (18)O, we show that the Hi-3 bands arise from coupling of two similar CO oscillators with one uncoupled frequency at approximately nu = 1917 cm(-1). Although in previous studies Lo-3 was not observed to recombine, by extending the observation range to 200-240 K, we found that recombination to Hi-3 does indeed occur, with an activation energy of approximately 6.5 kJ mol(-1). The frequencies of the Hi-3 bands suggest terminal CO ligation. This hypothesis was tested with DFT calculations on models with terminal CO ligands on Fe2 and Fe6 of the FeMo-cofactor. An S = 0 model with both CO ligands in exo positions predicts symmetric and asymmetric stretches at nu = 1938 and 1909 cm(-1), respectively, with relative band intensities of about 3.5:1, which is in good agreement with experiment. From the observed IR intensities, Hi-3 was found to be present at a concentration about equal to that of the EPR-active Hi-1 species. The relevance of Hi-3 to the nitrogenase catalytic mechanism and its recently discovered Fischer-Tropsch chemistry is discussed.

Cu(I)/O2 Chemistry Using a β-Diketiminate Supporting Ligand Derived from N,N-Dimethylhydrazine: A [Cu3O2]3+ Complex with Novel Reactivity

A Cu(I) complex, LCu(CH(3)CN), was prepared and characterized, where L(-) is a sterically unencumbered β-diketiminate ligand, the deprotonated version of 4-(2,2-dimethylhydrazino)dimethylhydrazone-3-penten-2-one (LH). Analysis of FTIR spectra of the products of the reaction of LCu(CH(3)CN) with CO indicate that L(-) is strongly electron donating, and support an equilibrium in solution between monomeric and dimeric forms with terminal and bridging CO ligands, respectively. Low temperature oxygenation of LCu(CH(3)CN) generated a bis(μ-oxo)tricopper complex with a S = 1 [Cu(3)O(2)](3+) core that was identified on the basis of UV-vis (λ(max) (ε, M(-1) cm(-1) per Cu) = 328 (10700), 420 (1500), 590 (835) nm) and X-band electron paramagnetic resonance (EPR) spectroscopy (Δm(s) = 2 transition at 1500 G), electrospray ionization (ESI) mass spectrometry, and spectrophotometric titration (0.35(2) equiv of O(2) per copper atom), magnetic susceptibility (μ(eff) = 2.8(1) BM), and H(2)O(2) detection experiments (no H(2)O(2) evolved upon acidification). Unlike other reported variants supported by neutral N-donor ligands, L(3)Cu(3)O(2) is not reduced by ferrocene, does not abstract H-atoms from phenols or 1,2-dihydroanthracene, oxidizes PPh(3) to Ph(3)P═O, and generates carbonate species upon exposure to CO(2). This unique reactivity for a [Cu(3)O(2)](3+) complex may be traced to the anionic charge and strong electron donating characteristics of L(-).

Silylation of Iron-Bound Carbon Monoxide Affords a Terminal Fe Carbyne

A series of monocarbonyl iron complexes in the formal oxidation states 0, +1, and +2 are accessible when supported by a tetradentate tris(phosphino)silyl ligand (SiP(iPr)(3) = [Si(o-C(6)H(4)PiPr(2))(3)](-)). X-ray diffraction (XRD) studies of these carbonyl complexes establish little geometrical change about the iron center as a function of oxidation state. It is possible to functionalize the terminal CO ligand of the most reduced carbonyl adduct by addition of SiMe(3)(+) to afford a well-defined iron carbyne species, (SiP(iPr)(3))Fe≡C-OSiMe(3). Single-crystal XRD data of this iron carbyne derivative reveal an unusually short Fe≡C-OSiMe(3) bond distance (1.671(2) Å) and a substantially elongated C-O distance (1.278(3) Å), consistent with Fe-C carbyne character. The overall trigonal bipyramidal geometry of (SiP(iPr)(3))Fe≡C-OSiMe(3) compares well with that of the corresponding carbonyls, (SiP(iPr)(3))Fe(CO)(-), (SiP(iPr)(3))Fe(CO), and (SiP(iPr)(3))Fe(CO)(+). Details regarding the electronic structure of the carbyne complex have been explored via the collection of comparative Mössbauer data for all of the complexes featured and also via DFT calculations. In sum, these data point to a strongly π-accepting Fischer-type carbyne ligand that confers stability to a low-valent iron(0) rather than high-valent iron(IV) center.

Structural diversity and magnetic properties in 1D and 2D azido-bridged cobalt(ii) complexes with 1,2-bis(2-pyridyl)ethylene

By utilizing a flexible co-ligand 1,2-bis(2-pyridyl)ethylene (2,2'-bpe), two new azido-bridged cobalt(II) complexes with the formulae [Co₃(N₃)₆(OH₂)₂(2,2'-bpe)₂](n)(2,2'-bpe)(n) (1) and [Co(N₃)₂(2,2'-bpe)₂](n) (2) have been synthesized and structurally characterized. Compound 1 shows an uncommon 1D chain comprised of double EO azido bridged five- and six-coordinated Co(II) geometries in a unique (-5-5-6-)(n) sequence of the coordination number. The 2,2'-bpe acts as a terminal co-ligand and an uncoordinated molecule in the crystal lattice. Moreover the adjacent 1D chain is assembled by C-Hπ interactions and the intermolecular hydrogen bonding between uncoordinated 2,2'-bpe and coordinated water molecules building a 2D layer. Whereas, compound 2 is a 2D coordination network containing the alternating double EO and double EE bridging modes of azides and ditopic 2,2'-bpe bridges. The magnetic investigation of 1 reveals dominant intra-chain ferromagnetic interactions, with the double EO azide-bridge and weak inter-chain antiferromagnetic interactions, with overall metamagnetic behaviour, having magnetic ordering at 6 K. The magnetic behaviour of 2 shows spin-canted antiferromagnetism below a T(N) of 12 K.

ChemInform Abstract: Palladium(I) Carbonyl Cation Catalyzed Carbonylation of Olefins and Alcohols in Concentrated Sulfuric Acid.

A new palladium catalyst was found to exhibit high catalytic activity for carbonylation of olefins and alcohols. cyclo-Bis(μ-carbonyl)dipalladium(I) cation (1) with bridging CO ligands is formed by reductive carbonylation of palladium sulfate, PdSO4, in concentrated H2SO4. When an olefin or alcohol is added, complex 1 changes to a new complex (2) with terminal CO ligands, and tertiary carboxylic acids are obtained in high yields at room temperature and atmospheric pressure of CO. IR and 13C NMR studies suggest that complex 2 may be tentatively formulated to be [Pd2(CO)2]2+, in which the terminal CO ligands are chemically equivalent. Complex 1 is a catalyst precursor, and complex 2 functions as an active species for the carbonylation of olefins and alcohols. The catalytic behavior of the palladium carbonyl catalyst supports the recently proposed reaction mechanism involving an olefin−metal−CO complex as an intermediate for the catalytic carbonylation of olefins and alcohols in strongly acidic solution.

μ-3-(8-Quinolyloxy)propanediyl]bis[dicarbonyl(η5-methoxycarbonylcyclopentadienyl)molybdenum(III)

The crystal structure of the title dimolybdenum complex, [Mo2(C12H9NO)(C7H7O2)2(CO)4], has a quasi-tetra­hedral Mo2C2 cluster core attached to one 3-(8-quinol­yloxy)propanediyl (L) and two methoxy­carbonyl­cyclo­penta­dienyl (Cp’) ligands which are coordinated to two Mo atoms: one Mo atom bonds two terminal CO ligands while the other links one terminal and one semi-bridging CO ligand. An intra­molecular C—H⋯N hydrogen bond results in the quinolyl plane of the L ligand approaching and being nearly perpendicular to one of the Cp’ rings [88.09 (12)°]. In the supra­molecular structure, a one-dimensional comb-shaped infinite chain is formed approximately along the crystallographic c axis by a combination of inter­molecular C—H⋯O hydrogen bonds and locally generates a C(6) motif. Finally, pairs of inversion-related comb-shaped chains associate into a new ladder-shaped infinite chain through weak π–π stacking inter­actions between neighbouring quinolyl systems (pyridyl centroid–centroid distance = 3.853 Å).

Oxidative addition of thiols to (CO)3Mo(μ-dppm)2Ru(CO)3 with formation of hydrido, bridged-thiolate complexes (dppm=Ph2PCH2PPh2)

Abstract The room temperature reactions of RSH (R = Et, Ph) with (CO)3Mo(μ-dppm)2Ru(CO)3 (1) in toluene yield (CO)2Mo(μ-SR)(μ-CO)(μ-dppm)2Ru(H)(CO) [R = Et (3); Ph (4)], which are characterized by elemental analysis, 1H NMR and IR spectroscopies and, in the case of 3, by X-ray crystallography. The complexes contain a trans,trans-Mo(μ-dppm)2Ru unit with a bridging thiolate, a terminal hydride at the Ru, three terminal CO ligands (two at the Mo, and one at the Ru), and one semi-bridged CO closer to the Mo.

Crystal structure, thermal stability and theoretical investigation on four 1,3-bis(1,2,4-triazol-1-yl)propane-based copper(II) complexes

Self-assembly of flexible 1,3-bis(1,2,4-triazol-1-yl)propane (btp), inorganic Cu(II) salt and rigid benzene-based carboxylate coligand generates four complexes, {[Cu(btp) 2(CH 3OH)(H 2O)]·H 2O·2ClO 4} n ( 1), {[Cu(btp)(Hbtc) 2]·0.5H 2O} n ( 2), [Cu(btp) 2(H 3btea) 2] n ( 3), and [Cu(btp)(nb) 2] ( 4) (H 3btc = 1,3,5-benzenetricarboxylic acid, H 4btea = 1,2,4,5-benzenetetracarboxylic acid, Hnb = p-nitrobenzoic acid), which are fully structural characterized by single-crystal X-ray crystallography, elemental analysis, IR, and TG–DTA techniques. Structural determinations reveal that the polymeric two-dimensional (2D) Cu-btp grid-like layer for 1, 1D linear single- and double-stranded chains for 2 and 3, as well as the discrete binuclear structure for 4, are jointly directed by the coordination polyhedrons of the Cu(II) ion and the exo-bidentate bridging btp core ligand with various conformations. The theoretical calculations suggest that the trans– trans btp is the most stable conformation, and the metal binding site is collectively determined by the electron density of N donors and the spatial orientation of the btp ligand. Unexpectedly, the polycarboxylate anions in 1– 4 can only act as terminal coligands not popular bridging connectors. The thermal stability of the resulting complexes is also compared.

Phosphane‐ and Phosphite‐Substituted Diiron Diselenolato Complexes as Models for [FeFe]‐Hydrogenases

AbstractThe displacement of terminal CO ligands in Fe2(μ‐Se2C3H5CH3)(CO)6 (1) by triphenylphosphane, trimethyl phosphite, and bis(diphenylphosphanyl)ethane (dppe) ligands is investigated. Treatment of 1 with 1 equiv. of triphenylphosphane afforded Fe2(μ‐Se2C3H5CH3)(CO)5(PPh3) (2). The mono‐ and disubstituted phosphite complexes Fe2(μ‐Se2C3H5CH3)(CO)5P(OMe)3 (3) and Fe2(μ‐Se2C3H5CH3)(CO)4[P(OMe)3]2 (4) were obtained from the reaction of 1 with excess P(OMe)3 at reflux in toluene. In contrast, the reaction of 1 with 1 equiv. of dppe in the presence of Me3NO·2H2O gave a mixture of Fe2(μ‐Se2C3H5CH3)(CO)4(κ2‐dppe) (5) and [Fe2(μ‐Se2C3H5CH3)(CO)5]2(μ‐dppe) (6). The newly synthesized complexes 2–6 were fully characterized by IR, 1H NMR, 13C NMR, 77Se{1H} NMR, and 31P{1H} NMR spectroscopy, mass spectrometry, elemental analysis, and X‐ray diffraction analysis. Complex 2 has proved to be a catalyst for the electrochemical reduction of the weak acid, acetic acid, to give molecular hydrogen. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Spin distribution of the H-cluster in the Hox–CO state of the [FeFe] hydrogenase from Desulfovibrio desulfuricans: HYSCORE and ENDOR study of 14N and 13C nuclear interactions

Hydrogenases are enzymes which catalyze the reversible cleavage of molecular hydrogen into protons and electrons. In [FeFe] hydrogenases the active center is a 6Fe6S cluster, referred to as the "H-cluster." It consists of the redox-active binuclear subcluster ([2Fe](H)) coordinated by CN(-) and CO ligands and the cubane-like [4Fe-4S](H) subcluster which is connected to the protein via Cys ligands. One of these Cys ligands bridges to the [2Fe](H) subcluster. The CO-inhibited form of [FeFe] hydrogenase isolated from Desulfovibrio desulfuricans was studied using advanced EPR methods. In the H(ox)-CO state the open coordination site at the [2Fe](H) subcluster is blocked by extrinsic CO, giving rise to an EPR-active S = 1/2 species. The CO inhibited state was prepared with (13)CO and illuminated under white light at 273 K. In this case scrambling of the CO ligands occurs. Three (13)C hyperfine couplings of 17.1, 7.4, and 3.8 MHz (isotropic part) were observed and assigned to (13)CO at the extrinsic, the bridging, and the terminal CO-ligand positions of the distal iron, respectively. No (13)CO exchange of the CO ligand to the proximal iron was observed. The hyperfine interactions detected indicate a rather large distribution of the spin density over the terminal and bridging CO ligands attached to the distal iron. Furthermore, (14)N nuclear spin interactions were measured. On the basis of the observed (14)N hyperfine couplings, which result from the CN(-) ligands of the [2Fe](H) subcluster, it has been concluded that there is very little unpaired spin density on the cyanides of the binuclear subcluster.

Reactions of triphenylphosphane-substituted ethoxycarbonylcarbene-bridged dicobalt carbonyl complexes with carbon monoxide or 13CO: An experimental and theoretical study

In CH 2Cl 2 solution and under a carbon monoxide atmosphere the cobalt complexes [μ 2-{ethoxycarbonyl(methylene)}-μ 2-(carbonyl)-bis(triphenylphosphanedicarbonyl-cobalt) ( Co–Co)] ( 4) and [μ 2-{ethoxycarbonyl(methylene)}-μ 2-(carbonyl)-(tricarbonyl-cobalt)-(triphenylphosphanedicarbonyl-cobalt) ( Co–Co)] ( 3) are in equilibrium. The equilibrium constant K = [ 3][PPh 3]/[ 4][CO] at 10 °C is 1.03 ± 0.11. The bridging and terminal CO ligands in complex 3 or 4 exchange with external 13CO simultaneously. In accord with that variable-temperature 13C NMR spectra reveal fluxional behavior for both complexes. The overall rate constant of 13CO-exchange for 3 at 10 °C is 17 × 10 −3 s −1 and for 4 at 10 °C is 26 × 10 3 s −1. In the case of complex 4 the concentration of PPh 3 has practically no influence on the rate of the 13CO-exchange reaction and on the rate of the reaction with CO. The coupling of the μ 2-ethoxycarbonylcarbene ligand and one of the coordinated carbon monoxide is at least one order of magnitude slower than the 13CO-exchange reactions, and is faster in complex 4 than in complex 3. The partial pressure of carbon monoxide has practically no effect on the coupling reaction.

Metal dicyanamide layered coordination polymers with cyanopyridine co-ligands: Synthesis, crystal structures and magnetism

A series of metal dicyanamide (dca) coordination polymers combined with cyanopyridine (cypy) terminal co-ligands, namely, [Co 2(dca) 4(4-cypy) 4] n ( 1), [Cd(dca) 2(4-cypy) 2] n ( 2), [Fe(dca) 2(3-cypy) 2] n ( 3) and [Co(dca) 2(3-cypy) 2] n ( 4), have been synthesized at the ambient conditions. X-ray single crystal diffraction reveals that complexes 1– 4 have similar metal-dca coordination layers in which the octahedral metal centers are connected by μ 1,5-dca linkers. Notably, three types of 3-D packing lattices are observed for these layered arrays. The thermal stabilities of such new crystalline materials have been studied by thermogravimetric analysis of mass loss. The magnetic properties of the Co II and Fe II complexes have been investigated and discussed in detail. A discrete mononuclear molecule [Cd(dca) 2(pyom) 2] ( 5) is also described, in which the chelated ligand O-methyl picolinimidate (pyom) arises from the addition of methanol solvent across the C N bond of 2-cypy.

Reactions of 13CO with Ethoxycarbonylcarbene‐Bridged Dicobalt Carbonyl Complexes: [μ2‐{Ethoxycarbonyl(methylene)}‐μ2‐(carbonyl)bis(tricarbonylcobalt)(Co–Co)] and [Di‐μ2‐{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(Co–Co)

AbstractIn a CH2Cl2 solution, under an atmospheric pressure of 13CO, the bridging and terminal CO ligands of the cobalt complex[μ2‐{ethoxycarbonyl(methylene)}‐μ2‐(carbonyl)bis(tricarbonylcobalt)(Co–Co)] (1) exchange with external 13CO at the same rate. The overall rate of CO exchange is kobs (10 °C) = 9.4 × 10–3 s–1 and kobs (25 °C) = (20.1 ± 1.2) × 10–3 s–1. In the presence of excess ethanol diethyl malonate (DEM), EtO213CCH2CO2Et is formed from 1 at a much smaller rate [kDEM (10 °C) = 0.40 × 10–5 s–1 and kDEM (25 °C) = (1.2 ± 0.1) × 10–5 s–1]. On the other hand, the complex [di‐μ2‐{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(Co–Co)](2) does not exchange its CO ligands for 13CO at all at 10 or 25 °C. In the presence of excess ethanol, diethyl malonate with natural isotopic distribution, and 13CO, ligands containing complex 1 are formed simultaneously and at the same rate, which is kobs (10 °C) = (15.2 ± 1.1) × 10–5 s–1 and kobs (25 °C) = (33.5 ± 1.8) × 10–5 s–1. Variable temperature 13C NMR spectra of 1 and 2 reveal fluxional behavior for both complexes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)